@TVSK AP is Access Point. when you click wireless scanner. below my neighbour AP. you can try this step "use a pin to press and hold the Reset pinhole button until all the LEDs flashed momentarily"

@TVSK Can you see your neighbour AP or own mobile phone hotspot ?

@TVSK Click 5GHz Wireless Scanner does any AP show (including your neighbour) if possible mobile phone temporarily switches on Hotspot select 5GHz only. If the AP shows Zero/None. *Recommend step If...

Maybe you can try setup RE650 1 meter from router (Tenda AC15) making sure device is not faulty (5Ghz). Than with extension cord gradually you move to 2M, 3M, ... 10M